Ultrasound imaging is used in medicine to examine tissue with sound signals at a frequency higher than the normal range of human hearing. To illustrate, engine noise from a typical truck might include 125 Hz sounds while birds may chirp at about 6,000 Hz. A typical intravascular ultrasound device might operate at 40,000,000 Hz (i.e., 40 MHz).
In medical ultrasound, a probe device sends sound waves through tissue. The sound waves bounce off features in the tissue and back to the transducer. The transducer converts the waves to an electrical signal and sends it to an image processing system. Typically, the image processing system converts the electrical signal to a digital signal, which can then be displayed on a computer monitor (allowing a doctor to see the patient's blood vessels) or stored for other analyses.
In fact, looking at the tissue is but one use of IVUS. Some IVUS systems are used to perform “virtual histology”, which involves analyzing an ultrasound signal to classify features in a patient's tissue (e.g., plaque, dead tissue, healthy tissue). IVUS can also be used to study the flow of blood within a patient. The velocity at which blood is flowing will typically produce a characteristic Doppler signature. This information can help identify is a patient is suffering from restricted blood flow due to, for example, atherosclerosis, or plaques.
The very fact that an IVUS signal may be put to more than one use is associated with challenges in the design and maintenance of IVUS systems. Any change in the signal processing that benefits one intended use can cause problems in another end-use. For example, in some ultrasound systems, transient resonances from the transducer produce signals, called ringdown, that detract from a visual display. A processing step can be added to the system that removes the ringdown from the signal. However, the ringdown signal does provide some data about the tissue that is useful in virtual histology. Thus, if the system is also used for virtual histology, yet another step must be added that puts the ringdown data back into the signal for the virtual histology application.
U.S. Patent Publication 2011/0087104 to Moore describes a system that “splits” the signal for imaging and for parametric (e.g., virtual histology) analysis. However, such a system requires duplicate, parallel hardware components that operate in tandem in the different signal processing pathways. Not only does duplicate internal hardware require additional design and manufacturing costs, it also raises some significant difficulties in subsequent modifications of the systems to add other image analysis tools.